NANOINDENTATION OF SOFT TISSUES AND OTHER BIOLOGICAL MATERIALS - Nanoindentation with Biological Applications - page 292

represent models of surfaces that prevent insect attachment. In the next
section, more examples will be provided of biomimetic materials
applications of nanoindentation.
3.3 . Acellular biological materials with biomimetic applications
An increasing interest in biomimetics, designing materials based on
natural biological structures, has led to another focus area of biomaterial
indentation: acellular biological materials. In order to design materials
that mimic nature, characterization of structure-property relationships in
natural materials down to the micro- or nano-scales is often necessary.
Indentation has become a valuable tool for characterizing mechanical
properties to complement the structural analyses also being performed at
small length scales.
One example of a biological material with desirable mechanical
properties is the nacre (mother-of-pearl) that lines mollusk shells. Nacre
is a material with extremely high fracture toughness that researchers
want to mimic when designing vehicle armor or other high impact
ceramics. Nacre is both strong and tough because it combines a strong
ceramic with a polymeric interface to provide toughness. The ceramic
plates, made up of aragonite, are typically 5-8 micrometers long and 200-
800 nm thick. 42 Because of these small dimensions, nanoindentation has
been used in conjunction with computational modeling to determine the
mechanical properties of the argonite blocks and the interfacial protein
that make up nacre's complex microstructure. 42,43 Spider silk is another
biomaterial of interest to researchers, due to its unusual combination of
high strength and toughness. Nanoindentation has been used to measure
anisotropic mechanical properties in two orthogonal planes in the 5
micrometer diameter spider dragline silk fibers using both quasi-static
indentation and dynamic stiffness imaging methods, as illustrated in
Fig. 9-3 . 9
Other biomimetics applications of nanoindentation have included
characterization of structure-property relationships in specific regions of
insect cuticle (exoskeleton), 41,44 mapping the variation in modulus and
hardness across the 200-600 micrometer diameter sponge spicule, 45